You need to use font name, not filename. Font name is inside the ttf file.
You can find font names for iOS here: http://iosfonts.com/
This code will list all your font names in your app, put it somewhere in viewDidLoad on main controller, run app and then in console found the right name for the font.
NSArray *familyNames = [[NSArray alloc] initWithArray:[UIFont familyNames]];
NSArray *fontNames;
NSInteger indFamily, indFont;
for (indFamily=0; indFamily<[familyNames count]; ++indFamily)
{
NSLog(@"Family name: %@", [familyNames objectAtIndex:indFamily]);
fontNames = [[NSArray alloc] initWithArray:
[UIFont fontNamesForFamilyName:
[familyNames objectAtIndex:indFamily]]];
for (indFont=0; indFont<[fontNames count]; ++indFont)
{
NSLog(@" Font name: %@", [fontNames objectAtIndex:indFont]);
}
}
Upd.
You can also right click on font file in Finder, get Info and copy full name. But it is not always 100%.